William Beveridge: The Old Testament fathers were saved by Christ the mediator

[Reformed Covenanter]

And as the enjoyment of God, and so everlasting happiness, was promised in the Old, as well as in the New Testament, so was it promised then too, as well as now, only in Jesus Christ; there being no other Mediator to reconcile God to us, and us to God, because none but he ever was or ever will be both God and man. And whosoever is God only and not man, or man only and not God, can never mediate betwixt God and man. For he that is God only cannot suffer for man; and he that is man only cannot make satisfaction to God: and therefore to make a person capable of suffering for man, and able to satisfy God, and so to mediate betwixt God and man, by suffering for the sins of the one, and satisfying the justice of the other; it is necessary that himself participate of both natures, which being joined together in one Person might so be reconciled to one another.

Now seeing there never was nor ever will be any such person in the world besides Christ, and seeing Christ was exactly such a person, perfect God and perfect man, it necessarily follows, that it was he, and he alone, that could be the Mediator betwixt God and man in the Old as well as in the New Testament: and so that whatsoever promises or overtures were made to the old Fathers were made only in him, without whom they could have enjoyed no mercy, nor have partaked any happiness, either in this world or that which is to come.

For the reference, see William Beveridge: The Old Testament fathers were saved by Christ the mediator.